The invention relates generally to the field of fluid driven turbines, such as wind turbines or water turbines, wherein electrical power is generated from airflow or water flow across rotor blades. More particularly, the invention relates to such turbines wherein the blades extend from a central rotating hub or shaft member to an annular rotating ring or rim member.
Wind turbines, also known as windmills, wind generators, wind machines or the like, are well known devices for producing energy, typically electrical energy, by harnessing the power of wind. Wind turbines used to generate large amounts of energy are very large structures, standing hundreds of feet tall and having rotor blades extending hundreds of feet, the rotor blades being mounted to a central hub or shaft. Large elongated blades are required since the area of blade sweep is proportional to the power that can be produced by a given wind turbine. This size creates a problem, in that each blade must act as a cantilever that can support the elongated blade and the blades must be increasingly massive toward the central hub in order to preclude the blade from breaking during use. Even with the use of high tech composites, carbon fibers and the like, a practical limit has been reached. For example, most large wind turbines have three blades, as this has been found to be the most efficient design. The desire to increase blade length in order to capture more wind is offset by the accompanying reduction in shaft revolutions per minute (rpm). Reduced rpm's require larger reduction gearboxes, which is undesirable. Decreasing blade pitch in order to increase the rpm's reduces torque, which is undesirable. Thus, known wind turbine designs always have to make sacrifices in order to balance these competing factors.
An alternative type of wind turbine incorporates an outer, annular ring or rim that is joined to the blades, such that the blade tips are no longer self-supporting and thereby allowing the blades to be longer. The blades extend from the central rotating hub or shaft to the annular rim and are therefore supported at both ends. In this embodiment, it is also known to utilize the rotational energy from the rotating annular rim rather than the central hub, since the annular rim travels at much faster speed. Rollers, wheels, gears, magnets or the like are used to transfer the rotational energy from the rim to one or more generator mechanisms or the like. Examples of such turbines are shown in U.S. Pat. No. 4,319,865 to Richard, U.S. Pat. No. 4,330,714 to Smith, U.S. Pat. No. 4,350,895 to Cook, U.S. Pat. No. 4,545,729 to Storm, U.S. Pat. No. 4,729,716 to Schmidt, and U.S. Pat. No. 6,664,655 to Vann. Such wind turbines are often of smaller size and utilize sails rather than blades in order to increase the number of wind catching elements, since the weight of the annular rim adds structural problems to the design.
It is an object of this invention to provide a highly efficient wind turbine, or water turbine, that allows desirable structural characteristics to be maximized, such as increased blade length, increased blade number, reduced blade weight, lowered cost of materials, increased rpm, increased torque, reduced noise and variable control of blade pitch, among others. It is a further object to provide such a turbine wherein the weight of the blades are reduced by structuring each blade as a relatively lightweight skin or sheet material disposed upon a plurality of cable members extending from a central rotating hub or shaft to an outer annular rim, wherein the cable members do the work of supporting the blades' skin and the outer annular rim. It is a further to provide such a turbine wherein, optionally, the pitch of the blades can be adjusted according to wind flow conditions.